Despite two decades of debate, there remains little consensus about what sustainability is, and how it should be achieved. Economists primarily portray sustainability as a macro-level concern, but there has been less attention on the implications of this social objective for policies related to the management of individual resources. This paper derives guidance for sector-level planning and project analysis from a macro-level norm of intergenerational fairness. Optimal sustainable management involves making tradeoffs between sectors. We derive a criteria for sector-level planning and project analysis that help make those tradeoffs without losing site of the sustainability goal.